1. Field of the Invention
The present invention relates to an ink container. More particularly, the invention relates to an ink container employed for an ink jet recording or the like which uses a liquid ink.
2. Related Background Art
In recent years, an ink jet recording apparatus has been used more widely because of its quiet movement, higher speed, and other features.
In the so-called on-demand type ink jet recording apparatus where ink droplets are discharged in accordance with image signals, it is desirable to keep the ink in the vicinity of the discharging ports in a state of a negative pressure which is slightly lower than the atmospheric pressure in order to avoid any ink leakage from the discharging ports of the recording head when the printing operation is at rest, and at the same time, to discharge it stably as the correctly sized ink droplets when the printing is in operation.
A conventional method which is most widely used for the purpose of creating this state is shown in FIG. 1. FIG. 1 is a perspective view illustrating the arrangement of the ink container for a printer according to the prior art.
In FIG. 1, an ink container 91 is installed in the apparatus independent of the recording head 92 which is mounted on a carriage and connected to the apparatus by tubes 94. Then, the water level of the ink therein is always kept at a position lower than the discharging ports of the recording head 92; thus implementing the state of a negative pressure.
In recent years, however, demands on smaller printers have been more conspicuous, leading to the development of a printer having the mode where an ink container is mounted on a carriage together with a recording head 92 rather than the system where the tubes 94 are drawn around. A printer of the kind is being put to practical use. However, the method for generating the negative pressure by the utilization of the difference in water levels as described above is not applicable to the printer having such a mode. Moreover, as a printer is made smaller, there is a tendency that it is carried more. Hence, it is prerequisite that no ink leakage should occur irrespective of the posture in which the small printer is carried. In other words, a means for generating an appropriate negative pressure must be provided for the ink container.
As an ink container to meet such a demand as this, the following is known:
At first, a porous material is filled in an ink container. Ink is soaked in the porous material to generate a negative pressure by the force of fine meniscus formed in the porous material.
Also, the opening of a container is covered with a dome-shaped flexible material to maintain a negative pressure by the deformation of the flexible material in response to the negative pressure thus generated in the container as described above (disclosed in Japanese Patent Application Laid-Open No. 59-98857).
Also, there is an ink container in which a movable wall is provided. FIGS. 2A to 2C are side cross-sectional views showing a conventional ink container of the kind.
In FIGS. 2A to 2C, a movable wall 110 is arranged in an ink container 111. The movable wall is being shifted toward the ink outlet 104 side as the quantity of the ink 103 is reduced due to printing. In this way, the negative pressure exerted on the ink in the main body of the ink container 111 is controlled by the friction on the sliding plane between the movable wall 110 and the inner surface of the main body of the ink container 111. In this respect, for the movable wall in FIGS. 2A to 2C, there is among others a type for which an O ring 105 is provided on the sliding plane of the movable wall 110 as shown in FIG. 2A; a type for which a flexible material of a diaphragm configuration is used for the movable wall 110 as represented in FIG. 2B; and a type for which a gel 106 is used for sealing the sliding plane of the movable wall as shown in FIG. 2C as already-applied by the applicant hereof.
However, when a recording head and an ink tank are mounted on a carriage, the carriage must be built as small as possible while securing the number of prints as many as possible. In other words, it should desirably be attempted to maximize the quantity of usable ink against the containable volume of the ink container (hereinafter referred to as application efficiency). In the case of the above-mentioned conventional examples such as the use of a porous material to soak ink, and a provision of a dome-shaped flexible material, there is a problem that the application efficiency is not very high although each of them demonstrates a good preventive property for the ink leakage.
On the other hands, when the conventional examples shown in FIGS. 2A to 2C are used, the application efficiency is considerable good for all of them. However, it is difficult for the systems represented in FIGS. 2A and 2B to reduce the force of the sliding friction while enhancing the water-tightness against the ink on the sliding plane simultaneously. Particularly, it is difficult to implement them constantly. Here, the application of the gel to the sliding plane as shown in FIG. 2C results in an extreme ease with which to adjust the sliding friction force in the sliding plane of the movable wall.
In an ink container using a movable wall such as this, the negative pressure is generated by the sliding friction force of the movable wall while in printing. Therefore, the negative pressure thus generated is dynamic, and it does not act in such a case where the meniscus of the discharging ports of the recording head is broken among some other cases. As a result, if the ink outlet 104 shown in FIG. 2C is placed downward by the posture of the printer, a water head H is exerted directly on the recording head to make the pressure greater than a pressure which is exerted when the posture is such that the ink outlet is placed upward. In such a case, the negative pressure given to the head differs by each of the postures; thus making it difficult to obtain a constant ink discharging condition. Moreover, there is still a possibility that an ink leakage takes place if the meniscus is broken due to the dust particles or the like which should abut on the discharging ports of the recording head.